U.S. patent number 10,658,663 [Application Number 15/695,050] was granted by the patent office on 2020-05-19 for electrode designs for lithium ion battery and capacitor hybrid system.
This patent grant is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS LLC. The grantee listed for this patent is GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to Jingjing Wu, Xiusheng Zhang.
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United States Patent |
10,658,663 |
Zhang , et al. |
May 19, 2020 |
Electrode designs for lithium ion battery and capacitor hybrid
system
Abstract
Lithium-utilizing electrochemical cells, providing hybrid
battery and capacitor activity, are formed of one or more lithium
battery anodes, optionally also including a capacitor electrode,
and one or more lithium battery cathodes, optionally with a
capacitor electrode, provided that there is at least one capacitor
electrode in the hybrid cell and that there are an equal number of
electrodes of opposing charge. The respective electrodes are formed
of porous layers of one of lithium anode material particles,
lithium cathode material particles, or compatible capacitor
material particles, formed on one or both sides of a compatible
current collector foil. The amounts of active battery and capacitor
particles are managed by the thickness of the porous coating
layers, and one-side or two-side electrode coatings, to balance the
capacities of the battery and capacitor particles to accept and
release lithium ions during repeated charging and discharging of
the hybrid cell.
Inventors: |
Zhang; Xiusheng (Shanghai,
CN), Wu; Jingjing (Shanghai, CN) |
Applicant: |
Name |
City |
State |
Country |
Type |
GM GLOBAL TECHNOLOGY OPERATIONS LLC |
Detroit |
MI |
US |
|
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS
LLC (Detroit, MI)
|
Family
ID: |
65517530 |
Appl.
No.: |
15/695,050 |
Filed: |
September 5, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190074510 A1 |
Mar 7, 2019 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01G
11/46 (20130101); H01M 2/16 (20130101); H01G
11/32 (20130101); H01G 11/34 (20130101); H01M
4/13 (20130101); H01M 4/587 (20130101); H01M
10/0525 (20130101); H01M 4/663 (20130101); H01G
11/26 (20130101); H01M 4/505 (20130101); H01M
10/0587 (20130101); H01M 4/485 (20130101); H01G
11/00 (20130101); H01G 11/06 (20130101); H01M
4/405 (20130101); H01G 11/30 (20130101); H01M
2220/20 (20130101); H01M 2004/028 (20130101) |
Current International
Class: |
H01M
4/505 (20100101); H01G 11/00 (20130101); H01M
4/13 (20100101); H01M 4/587 (20100101); H01M
4/485 (20100101); H01M 2/16 (20060101); H01M
4/66 (20060101); H01M 4/40 (20060101); H01M
10/0525 (20100101); H01M 10/0587 (20100101); H01M
4/02 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Liu et al., U.S. Appl. No. 15/221,963 entitled "Hybrid Cell Design
of Alternately Stacked or Wound Lithium Ion Battery and Capacitor
Electrodes," filed Jul. 28, 2016. cited by applicant.
|
Primary Examiner: Park; Lisa S
Attorney, Agent or Firm: Reising Ethington P.C.
Claims
The invention claimed is:
1. An electrochemical cell comprising an assembly of at least two
pairs of stacked or wound rolls of facing electrodes of opposed
electrical charge, each electrode consisting of a two-sided current
collector foil coated on one or both sides with a porous layer of
particles of an electrode material, each coated layer of electrode
material being one selected from the group consisting of (i) a
lithium ion intercalating/de-intercalating anode material, (ii) a
lithium ion intercalating/de-intercalating cathode material, and
(iii) a lithium ion, or compatible electrolyte anion,
adsorbing/desorbing capacitor material, the porous layers of each
electrode material being separated from each other by the two-sided
current collector foil and from a directly facing layer of an
electrode by a co-extensive porous separator layer, the porous
layers of each electrode material and each separator being
infiltrated with a non-aqueous liquid electrolyte of lithium ions
and compatible anions; the at least two pairs of stacked or wound
rolls of facing electrodes of opposite charge comprising an outer
coated layer of electrode material at each end of the stack or
wound roll with each of the other coated layers of electrode
material being internal with respect to the outer coated layers of
electrode material; the porous layers of electrode material that
are coated separately on each two-sided current collector foil
being selected from the group consisting of: (i) a layer of
lithium-ion anode material on one or both sides of the current
collector foil, (ii) a layer of lithium-ion cathode material on one
or both sides of the current collector foil, and (iii) a layer of
capacitor material on one or both sides of the current collector
foil; the assembly of at least two pairs of facing, opposing
electrical charge electrodes including at least one electrode
coating layer of capacitor material facing at least one layer of
opposing lithium-ion anode material or at least one layer of
opposing lithium-ion cathode material, the measured lithium
ion-adsorbing or anion-adsorbing capacity of the capacitor material
and the measured lithium ion accepting capacity of the anode or
cathode material being in the ratio range of 0.8-1.2; the at least
two pairs of stacked or wound rolls of facing electrodes of
opposite charge comprising a majority of the electrode coating
layers of capacitor material which are located internally with
respect to the outer layers of coated electrode materials; and the
layers of electrode material on the at least two pairs of opposing
electrodes being selected to obtain a predetermined combination of
energy density (Wh/kg) and power density (W/kg) for the
electrochemical cell.
2. An electrochemical cell as stated in claim 1 in which the anode
material is lithium titanate, the cathode material is lithium
manganese oxide, and the capacitor material is activated
carbon.
3. An electrochemical cell as stated in claim 1 in which the
electrochemical cell comprises two to four positive-charge
electrode members interposed with a like number of negative-charge
electrode members, at least one of the electrode members being a
particulate capacitor composition directly facing a battery
electrode composition of the opposite charge, the measured lithium
ion accepting capacity of the capacitor material and the measured
lithium ion accepting capacity of the battery composition material
being in the ratio range of 0.8-1.2.
4. An electrochemical cell as stated in claim 3 in which the anode
material is lithium titanate, the cathode material is lithium
manganese oxide, and the capacitor material is activated
carbon.
5. An electrochemical cell as stated in claim 1 in which the
electrochemical cell comprises two to four positive-charge
electrode members interposed with a like number of negative-charge
electrode members, at least one of the electrode members being a
particulate capacitor composition directly facing an anode
composition of the opposite charge, the measured lithium ion
accepting capacity of the capacitor material and the measured
lithium ion accepting capacity of the anode composition material
being in the ratio range of 0.8-1.2.
6. An electrochemical cell as stated in claim 5 in which the
capacitor material is activated carbon and the anode material is
lithium titanate.
7. An electrochemical cell as stated in claim 1 in which the
electrochemical cell comprises three positive charge electrode
members and three negative charge electrode members, a positive
charged capacitor electrode directly facing a negative charged
capacitor electrode, an anode electrode directly facing the
positive charge capacitor electrode, and a cathode electrode
directly facing the negative charge capacitor electrode, and the
capacitor electrodes having equal ion absorbing capacity.
8. An electrochemical cell as stated in claim 7 in which the
capacitor material is activated carbon, the anode material is
lithium titanate, and the cathode material is lithium manganese
oxide.
9. An electrochemical cell as stated in claim 1 comprising two
negative charge anodes with a positive charge capacitor electrode
placed between them and a cathode placed directly facing one of the
anodes, the thickness of the anode material on the side of each
anode facing the capacitor electrode being less than the thickness
of the anode material on the opposite sides of their respective
current collectors.
10. An electrochemical cell as stated in claim 9 in which the
capacitor material is activated carbon, the anode material is
lithium titanate, and the cathode material is lithium manganese
oxide.
11. An electrochemical cell as stated in claim 1 in which the
electrochemical cell comprises three positive charge electrode
members and three negative charge electrode members in which a
positive charged capacitor electrode is directly facing a negative
charged capacitor electrode, an anode electrode is directly facing
the positive charge capacitor electrode, and a cathode electrode is
directly facing the negative charge capacitor electrode, the
capacitor electrodes having equal ion absorbing capacity, the
thickness of the anode material on the side of the anode electrode
directly facing the positive charge capacitor electrode being less
than the thickness of the anode material on the other side of its
anode current collector, and the thickness of the cathode material
on the side of the cathode directly facing the negative charge
capacitor being less than the thickness of the cathode material on
the other side of its cathode current collector.
12. An electrochemical cell as stated in claim 11 in which the
capacitor material is activated carbon, the anode material is
lithium titanate, and the cathode material is lithium manganese
oxide.
13. An electrochemical cell as stated in claim 1 in which the
electrochemical cell comprises three negative charge anodes, two of
the anodes being one side-coated, and two positive charge cathodes,
one of which is one side-coated, and a positive charge one
side-coated capacitor, the cell being assembled with an uncoated
side of an anode directly facing an uncoated side of the capacitor,
the coated side of the second anode directly facing the coated side
of the capacitor, and the uncoated side of the cathode directly
facing the uncoated side of the second anode.
14. An electrochemical cell as stated in claim 13 in which the
capacitor material is activated carbon, the anode material is
lithium titanate, and the cathode material is lithium manganese
oxide.
15. An electrochemical cell as stated in claim 1 in which the
electrochemical cell comprises two anode members and a negatively
charged capacitor member alternately interposed with two cathode
members and a positively charged capacitor member, the
oppositely-charged capacitor members being adjacent electrode
members with an anode member adjacent to the positively charged
capacitor and a cathode member adjacent to the negatively charged
capacitor member; the capacitor members, one anode member, and one
cathode member each being coated with a porous layer of active
electrode particles on only one side of the current collector for
the electrode, the coated side of each capacitor directly facing
each other, the uncoated side of the one anode member directly
facing the uncoated side of the positively charged capacitor and
the uncoated side of the one cathode member directly facing the
negatively charged capacitor.
16. An electrochemical cell as stated in claim 15 in which the
capacitor material is activated carbon, the anode material is
lithium titanate, and the cathode material is lithium manganese
oxide.
17. A lithium-ion electrochemical cell comprising an assembly of at
least two pairs of stacked or wound rolls of facing electrodes of
opposed electrical charge, each electrode consisting of a two-sided
current collector foil coated on one or both sides with a porous
layer of particles of an electrode material selected from the group
consisting of (i) a lithium ion intercalating/de-intercalating
anode material, (ii) a lithium ion intercalating/de-intercalating
cathode material, and (iii) a lithium ion, or compatible
electrolyte anion, adsorbing/desorbing capacitor material, the
porous layers of each electrode material being separated from each
other by the two-sided current collector foil and from a facing
layer of an electrode by a co-extensive porous separator layer, the
porous layers of each electrode material and each separator being
infiltrated with a non-aqueous liquid electrolyte of lithium ions
and compatible anions; the electrochemical cell being further
characterized by the at least two pairs of stacked or wound rolls
of facing electrodes of opposite charge comprising an outer coated
layer of electrode material at each end of the stack or wound roll
with each of the other coated layers being internal with respect to
the outer coated layers; an internal anode material electrode
directly facing an internal capacitor material electrode of the
opposite electrical charge, the measured lithium ion accepting
capacity of the anode material electrode and the measured anion
adsorbing capacity of the capacitor material being in the ratio
range of 0.8-1.2.
18. An electrochemical cell as stated in claim 17 in which the
anode material is lithium titanate and the capacitor material is
activated carbon.
19. A lithium-ion electrochemical cell comprising an assembly of at
least two pairs of stacked or wound rolls of facing electrodes of
opposed electrical charge, each electrode consisting of a two-sided
current collector foil coated on one or both sides with a porous
layer of particles of an electrode material selected from the group
consisting of (i) a lithium ion intercalating/de-intercalating
anode material, (ii) a lithium ion intercalating/de-intercalating
cathode material, and (iii) a lithium ion, or compatible
electrolyte anion, adsorbing/desorbing capacitor material, the
porous layers of each electrode material being separated from each
other by the two-sided current collector foil and from a facing
layer of an electrode by a co-extensive porous separator layer, the
porous layers of each electrode material and each separator being
infiltrated with a non-aqueous liquid electrolyte of lithium ions
and compatible anions; the electrochemical cell being further
characterized by the at least two pairs of stacked or wound rolls
of facing electrodes of opposite charge comprising an outer coated
layer of electrode material at each end of the stack or wound roll
with each of the other coated layers being internal with respect to
the outer coated layers; an internal cathode material electrode
directly facing an internal capacitor material electrode of the
opposite electrical charge, the measured lithium ion accepting
capacity of the cathode and the measured ion adsorbing capacity of
the capacitor material electrode being in the ratio range of
0.8-1.2.
20. An electrochemical cell as stated in claim 19 in which the
cathode material is lithium manganese oxide and the capacitor
material is activated carbon.
Description
TECHNICAL FIELD
Lithium-ion battery anodes and cathodes, formed of a porous layer
of anode or cathode material particles on one or both sides of a
current collector foil, are used in combination with one side or
two side-coated lithium ion-adsorbing capacitor electrodes to form
hybrid electrochemical cells. Combinations of the porous battery
electrodes and capacitor electrodes are prepared and arranged with
inter-placed porous separators and infiltrated with a non-aqueous
lithium ion-conducting electrolyte solution to provide a
predetermined combination of battery and capacitor capacities in
each such individual hybrid cell. The capacities of battery anode
materials and capacitor cathode materials in the cells are
proportionally balanced to best utilize the flow of lithium ions in
each cell. The capacity, coulombic efficiency, and life of the
hybrid cells are thereby increased.
CROSS-REFERENCE TO RELATED APPLICATION
The content of the subject patent application provides improvements
to the operation of the hybrid cell designs disclosed in co-pending
application Ser. No. 15/221,963, filed Jul. 28, 2016, and titled
Hybrid Cell Design of Alternately Stacked or Wound Lithium Ion
Battery and Capacitor Electrodes. This co-pending application is
assigned to the same assignee as subject application. Portions of
the text of the earlier co-pending application are included in the
subject specification.
BACKGROUND OF THE INVENTION
The material presented as background information in this section of
the specification is not necessarily prior art.
Electric-powered automotive vehicles use multi-cell batteries to
provide electrical energy for providing electrical power for
driving the vehicle and for providing electrical energy to many
devices on the vehicle. Batteries comprising many lithium-ion
electrochemical cells are examples of such electrical power
sources. And such batteries are used in many non-automotive
applications.
In some applications, it may be useful to combine a lithium-ion
battery with a capacitor. For example, such capacitors may be
charged during braking of the vehicle and the stored electrical
charge used in recharging cells of the lithium-ion battery.
There is a need for a practice to jointly package and employ cells
for lithium-ion batteries and such capacitors for efficiency in
their mutual interconnection and interaction.
SUMMARY OF THE INVENTION
In accordance with practices of this invention, anode and cathode
materials for lithium-ion batteries are used in varying
combinations with compatible capacitor materials to form electrodes
for hybrid electrochemical cells to conveniently provide different
predetermined combinations of lithium-ion battery properties and
capacitor properties. Such combinations of lithium ion battery
electrodes and capacitor electrodes can be readily adapted and
arranged to produce different, useful combinations of energy
densities (Wh/kg) and power densities (W/kg) in a hybrid
electrochemical cell that better adapts its use in different
applications. In the following text, the anode is often referred to
as the negative electrode (as it is during cell discharge) and the
cathode is often referred to as the positive electrode (as it is
during cell discharge). One or more capacitor electrodes are
grouped with the battery anode electrodes and/or the battery
cathode electrodes. The capacitor material electrode(s) will have
the same charge as the battery electrode with which it is
electrically connected in the hybrid cell. In each hybrid cell of
this invention there will be at least two electrically-connected
negative electrodes and two electrically-connected positive
electrodes. And there will be an equal number of negative and
positive electrodes in the hybrid cell. For example, a hybrid
electrochemical cell may consist of two negative electrodes of
lithium intercalating anode material and one positive electrode of
lithium-intercalating cathode material and one negative electrode
of capacitor material.
In accordance with a further aspect of this invention, detailed
attention is given to balance the flow of lithium ions through the
electrolyte of the hybrid cell between battery electrodes and
capacitor electrodes of opposing electrical charge. This is
accomplished by adjusting the amounts and locations of the
respective electrode materials so as to proportion the lithium-ion
adsorbing or utilizing capacity of the electrode materials which
are releasing and adsorbing lithium ions during each charge and
discharge cycle of the hybrid cell.
In general, each electrode is formed of a suitable current
collector foil that is coated on one or both sides with a porous
layer of micrometer-size particles of active lithium ion battery
anode particles, or of lithium ion battery cathode particles, or
with a porous layer of like-wise sized capacitor particles.
Each such one-side or two-side coated electrode is typically less
than a millimeter in thickness. And each electrode is shaped in its
other two dimensions so that alternating positively charged and
negatively charged electrodes may be assembled with interposed,
thin, porous separator layers in the formation of a hybrid
battery/capacitor electrochemical cell. Such a hybrid cell may be
formed of a stack of equal numbers of like-shaped (typically
rectangular shaped) alternating positive and negative electrodes
and separators. In a different cell assembly method, the cell may
be formed by winding like-shaped (typically long rectangular
strips) alternating two-sided positive and negative electrodes and
separators layers into rolled assemblies. In an assembled, formed
cell, the micro-pores of the alternating electrodes and separators
are filled with a lithium cation-conducting electrolyte composed of
one or more lithium salts (such as LiPF.sub.6) dissolved in a
non-aqueous liquid electrolyte that functions at the required
operating temperature range of the hybrid cell.
By way of illustrative examples, suitable anode materials include
graphite particles or lithium titanate particles
(Li.sub.4Ti.sub.5O.sub.12, LTO); a suitable cathode material is
particles of LiMn.sub.2O.sub.4 (LMO),
LiNi.sub.xMn.sub.yCo.sub.(1-x-y)O.sub.2 (NMC) or particles of
LiFePO.sub.4 (LFP); and a suitable capacitor material is particles
of activated carbon. In the operation of a cell the anode particles
and cathode particles interact with the electrolyte to alternately
intercalate and de-intercalate lithium ions (Li+), positively
charged capacitor electrode particles alternately adsorb and desorb
anions (such as PF.sub.6.sup.-), and negatively charged capacitor
electrode particles alternately adsorb and desorb cations (such as
Li.sup.+). The hybrid system has two types of capacitor
arrangements. One is where the capacitor electrode is connected
with a battery electrode (LIC). For example, if an anode electrode
(LTO particles) is connected with a capacitor (AC particles), the
anode will alternately intercalate and de-intercalate lithium ions
and the capacitor will de-absorb and absorb corresponding anions
(e.g., PF.sub.6.sup.-) during charge/discharge. Another capacitor
assembly is an electrochemical double layer capacitor (EDLC) in
which both electrodes are capacitors (which are further paired with
a battery electrode or electrodes in a hybrid cell). In an EDLC,
the cathode capacitor absorbs/desorbs PF.sub.6.sup.- and the anode
capacitor adsorbs/desorbs Li.sup.+ during the repeated
charge/discharge cycling.
In general, the process of intercalation/de-intercalation occurs
throughout the whole volume of the selected particulate battery
electrode material. A gram of battery electrode material can
usually intercalate a greater amount of lithium ions than are
adsorbed on the surfaces of a like amount of capacitor particles.
But the release of lithium ions from battery electrode particles is
typically slower than the release of lithium ions from selected
capacitor particles. The battery particles are typically capable of
producing a greater energy density (Wh/kg) per gram than capacitor
particles, but the capacitor particles release adsorbed lithium
ions faster and are typically capable of providing a greater power
density (W/kg) than battery particles.
The amounts of the respective electrode materials are determined by
the cell design with its intended energy density and power density.
The selected compositions of the anode, cathode, and capacitor
materials have known molar or weight capacities to interact with
the lithium anions and the cations of the selected electrolyte. And
the observed capacities of the particles of the electrode
materials, in their bonded layers on a current collector foil may
be confirmed experimentally. The capacity of battery electrode
material may be determined by its molar content (mAh/g) and actual
weight loading. The capacity and amount of capacitor material may
also be determined by its molar content or weight. Sometimes an N/P
ratio is used in this specification. The N/P ratio refers to the
negative electrode capacity (anode during cell discharge) to
positive electrode capacity (cathode capacity).
Sometimes it is convenient to devise or prepare a hybrid cell
starting with an existing design of a lithium-ion battery cell. The
respective amounts of anode and cathode electrode materials are
known and their function demonstrated. And often the electrode
members of the existing battery cell have been organized and
prepared to have substantially equal thicknesses for the assembly
of the cell packages making up the battery. The required strategy
in making a new hybrid cell, or to convert an existing battery cell
to a hybrid cell, is to determine the locations and amount(s) of
capacitor materials to be used in preparing the electrode members
for a desired hybrid cell of desired energy and power densities. It
is recognized herein that the molar (or weight) capacity of battery
electrode materials to react with the electrolyte to intercalate
and de-intercalate lithium ions and corresponding anions
significantly exceeds the molar or weight capacities of useful
capacitor material particles to absorb and de-absorb the same ions
in the same electrochemical cell environment. We have found that it
is necessary to balance the ion-utilizing capacities of the
respective electrodes in order to best utilize the potential
advantages and properties of a hybrid lithium-ion battery/capacitor
cell. In order to suitably balance the respective capacities (for
example, to balance the N/P ratio) of the electrodes of the hybrid
cell, several structural changes are disclosed and illustrated in
this specification. Mismatches in the relative amounts and
thicknesses of battery electrode materials and capacitor electrode
materials must be accommodated in the design and assembly of the
electrodes of a hybrid lithium-ion battery/capacitor cell.
In accordance with practices of this invention, specific attention
is given to the relative capacities of a particulate battery anode
material or a particulate cathode material and an adjoining
capacitor electrode material of opposite electrical charge. Each
anode and cathode needs to receive and properly utilize all of the
incoming lithium ions, as interacting electrode members in a common
hybrid cell formed of lithium battery electrodes (sometime referred
to herein as LIB) and capacitor electrodes (LIC or EDLC). It is
necessary that each material-coated side of each battery electrode
receives the quantity of lithium ions that it can assimilate and
utilize. Otherwise, the operation of the hybrid cell is
compromised.
But first we proceed with a description of the electrode members of
the hybrid cells.
In a first embodiment of this invention, four different cell units
serve as basic elements for combining into a hybrid cell design of
lithium ion battery electrodes and capacitor electrodes. Each
individual cell unit is formed of at least two electrodes, each
with a porous layer of the same particulate electrode material
coated on one or both sides of a compatible current collector foil.
The two electrodes are aligned side-by-side with facing electrode
layers separated by a porous separator member. And the respective
units are like-shaped or shaped complimentarily so that they can be
assembled in a predetermined relationship in a stack, or wound in a
roll, to form a hybrid lithium-ion battery and capacitor
electrochemical cell.
A first cell unit (Unit A) is formed of a two-side coated cathode
and a two-side coated anode for a lithium-ion battery. The anode is
negatively charged and the cathode positively charged when the cell
is being discharged. A second cell unit (Unit B) is formed of a
two-sided capacitor positive electrode and a two-sided capacitor
negative electrode with an interposed separator. A third cell unit
(Unit C) is formed of a two-sided cathode electrode (+) and a
two-sided capacitor electrode (-) with an interposed porous
separator. And a fourth cell unit (Unit D) is formed of a two-sided
anode electrode (-) and a two-sided capacitor electrode (+) with an
interposed separator. For purposes of illustration: particles of
graphite or LTO may be used as a battery anode material; particles
of NMO or NMC may be used as a battery cathode material; and
particles of activated carbon may be used in each capacitor
electrode.
Combinations of two or more of these cell unit types are combined
to form a hybrid cell design combining at least one battery
electrode and one capacitor electrode. For example, a combination
of cell Units A and C (with an interposed separator) provides a
combination of a lithium ion battery cell (LIB) and a lithium
capacitor cell (LIC) using a battery cathode material and a
capacitor electrode. In their charged state, the two anode
electrodes are negatively charged and the cathode electrode and
capacitor electrode are positively charged. Depending on the
compositions and relative amounts of the respective electrode
materials, this hybrid combination of cell Units A and C can
provide a useful combination of battery energy density and
capacitor power density.
As a second illustrative example, a combination of three cell units
A, C, and C in a hybrid electrochemical cell provides a combination
of a lithium-ion battery cell with two cells using a battery
cathode material and capacitor counter-electrodes. In its charged
state, the overall combination of units provides a cell with three
positively charged battery cathode electrodes, a negatively charged
battery anode electrode and two negatively charged capacitor
electrodes. This hybrid cell combination, with two negatively
charged capacitor electrodes, can provide a different useful
combination of battery energy density and capacitor power
density.
In a third illustrative example, a combination of four cell units,
C, D, D, and B, in a hybrid electrochemical cell provides a
combination of a cathode (+)/capacitor (-) cell, two anode
(-)/capacitor (+) cells, and a capacitor (+)/capacitor (-) cell in
its charged state. And this cell combination, with one battery
cathode, two battery anodes, two negatively charged capacitor
electrodes, and three positively charged capacitor electrodes, can
provide still a different useful combination of battery energy
density and capacitor power density.
The energy density and power density of a specific combination of
the above described cell units (A), (B), (C), and (D) will depend
on the specific electrode materials selected and the loadings of
the materials in the electrodes. In general, an increase in the
amount of the two-side coated capacitor positive electrode material
and two-side coated capacitor negative electrode material (cell
unit B) will increase the power density of a hybrid cell. An
increase in the amount of cell unit A will increase the energy
density of a hybrid cell. And combinations of cell units, C and D,
can be used to balance the energy and power performance of a
cell.
Such hybrid combinations of cell units may be formed by the
stacking of individual (typically rectangular shaped) cell units
with interposed separators, or by the rolling of an arranged
assembly of like-shaped, elongated, cell units with interposed
separators.
But it is found that the capacities of the electrode members and
the capacitor members to accept and use lithium ions in the
combined cell units is preferably balanced in order to take
advantage of the benefits of the unique structures of the cell
members. For example, when a hybrid cell is formed of a stacked
assembly of two or more LTO battery anode members and a
corresponding number of LMO battery cathode member(s) and activated
carbon (AC) capacitor electrode(s), provision is to be made to
manage the flow of lithium ions between the electrodes during
charging and discharging of the hybrid cell. The balance of such
lithium ion exchange capacities is of particular concern in
locations where a battery electrode is facing a capacitor electrode
of opposing charge. In the hybrid cell, the stacked electrodes,
each consisting of two porous electrode layers bonded to opposite
surfaces of a current collector foil, are physically spaced with a
thin porous polymeric separator (e.g., about ten micrometers thick)
and the pores of each of the electrode layers and the separators
are fully infiltrated with an electrolyte (for example a solution
of LiPF.sub.6 in a mixture of organic solvents).
During charging of the cell members, lithium ions are
de-intercalated from the LMO cathode and de-absorbed from the AC
capacitor, flow through the electrolyte, and intercalated into the
LTO anode material as PF.sub.6.sup.- anions flow through the
electrolyte in the opposite direction between the electrodes. It is
found that there is a need to balance the respective capacities of
the active materials of the LTO anodes and of the AC and LMO
cathodes to receive and chemically accept lithium ions. It is
desired to minimize excessive diffusion of lithium ions on or into
any of the electrode materials. As will be shown further in this
specification, the capacities to receive and manage lithium ions by
the respective capacitor electrodes and battery electrodes are
preferably carefully balanced in order to maintain the operating
efficiencies and lives of the hybrid cells. For example, in an
assembly of at least one pair of facing, opposing electrical charge
electrodes including at least one electrode coating layer of
capacitor material facing at least one layer of opposing
lithium-ion battery anode material or at least one layer of
opposing cathode material, the measured lithium ion accepting
capacity of the capacitor material and the measured lithium ion
accepting capacity of the anode or cathode material is in the ratio
range of 0.8-1.2. In other words, the weight or molar amount of the
battery electrode material and the capacitor material, infiltrated
with the same liquid electrolyte and spaced a few micrometers from
each other by a porous separator, are determined such that the
lithium ions flowing between the particulate electrode materials
are suitably and fully utilized.
Other objects and advantages of the invention will be apparent from
specific illustrations of practices of the invention which follow
below in this specification.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-1D are schematic side views of four cell units of two
opposing electrodes for use in forming hybrid electrochemical cells
in accordance with one embodiment of this invention. The end
surfaces of each electrode and its separator are distinguished with
slanted lines or with dots so as to better distinguish the
different elements of each electrode. Each illustrated cell unit is
formed of an upstanding current collector foil with a connector tab
extending upwardly from the top side of the foil. A porous layer of
a particulate electrode material is bonded to each major face of
the current collector foil. The positive (+) and negative (-) signs
above the current collector tabs indicates the electrical charge of
the charged electrode in the cell unit (as it is being discharged).
A porous separator layer separates facing sides of the electrodes.
FIG. 1A illustrates the first cell unit (10) is formed of
positively-charged cathode material for a lithium-ion battery cell
and negatively charged anode material. FIG. 1B illustrates the
second cell unit (12) which is formed of positively charged
capacitor material (+) and negatively charged capacitor material
(-). FIG. 1C illustrates the third cell unit (14) which is formed
of Li-battery cathode material (+) and capacitor material (-). FIG.
1D illustrates a fourth unit cell formed of positively charged
capacitor material (+) and negatively charged anode material
(-).
FIGS. 2A through 2C are schematic side views of three groups of
stacked hybrid assemblies of two or more of the individual cell
units illustrated in FIGS. 1A-1D. Viewed from left to right in FIG.
2A, the first hybrid grouping is formed of individual cell units 10
and 16 (as illustrated in FIGS. 1A and 1D). In FIG. 2B, the second
hybrid electrochemical cell grouping is formed of individual cell
units 14, 14, and 10 as illustrated in FIGS. 1C and 1A. And in FIG.
2C, the third hybrid electrochemical cell grouping is formed of
individual cell units 14, 16, 16, and 12 as illustrated in FIGS.
1C, 1D, and 1B. In an assembled hybrid cell, the porous electrode
members would be closely stacked against the interposed porous
separators, and the porous members infiltrated with a non-aqueous
solution of a lithium electrolyte.
FIG. 3A is a schematic side-view of a modified version of the
hybrid grouping of FIG. 2A. In FIG. 3A, two lithium titanate (LTO)
anodes are paired with a lithium manganese oxide (LMO) battery
cathode and an activated carbon (AC) capacitor cathode. The LTO
anode members are electrically connected and indicated as
negatively charged, as they would be when the hybrid cell is being
discharged. The LMO battery cathode and AC capacitor cathode are
electrically connected and indicated as positively charged. As will
be explained below in this specification, the amount of activated
carbon in the capacitor cathode has been increased for the purpose
of equalizing the flow of lithium ions during the charging of the
hybrid cell. For purposes of simplifying the illustration of the
hybrid cell, the separators which would be placed between the
electrodes in a closely stacked assembly are not shown, and the
liquid electrolyte that would be infused into the pores of the
electrode materials and the separators is not illustrated.
FIG. 3B is a schematic side-view of a modified version of the
hybrid grouping of FIG. 2B. In FIG. 3B, two lithium titanate (LTO)
anodes and an activated carbon capacitor anode are assembled with
two LMO cathodes and an activated carbon capacitor cathode. The
anode members are electrically connected and indicated as
negatively charged. The cathode members are electrically connected
and indicated as positively charged. The amount of activated carbon
in each of the capacitor anode and the capacitor cathode has been
increased for the purpose of equalizing the flow of lithium ions
during the charging of the hybrid cell. Again, in a fully assembled
hybrid cell, separators would be placed between the electrodes in a
closely stacked assembly and an liquid electrolyte would be infused
into the pores of the electrode materials and the separators.
FIG. 4A is a simplified schematic side-view of a second modified
version of the hybrid grouping of FIG. 2A. In FIG. 4A, two lithium
titanate (LTO) anodes are paired with a lithium manganese oxide
(LMO) battery cathode and an activated carbon (AC) capacitor
cathode. The LTO anode members are electrically connected and
indicated as negatively charged as they would be when the hybrid
cell is being discharged. The LMO battery cathode and AC capacitor
cathode are electrically connected and indicated as positively
charged. As will be explained below in this specification, the
amount of active LTO particles on one side of each of the LTO
anodes has been reduced, and amount of activated carbon in each
side of the capacitor cathode has been increased. Each modification
is for the purpose of equalizing the flow of lithium ions during
the charging of the hybrid cell.
FIG. 4B is a simplified schematic side-view of a second modified
version of the hybrid grouping of FIG. 2B. In FIG. 4B, two lithium
titanate (LTO) anodes and an activated carbon capacitor anode are
assembled with two LMO cathodes and an activated carbon capacitor
cathode. The anode members are electrically connected and indicated
as negatively charged. The cathode members are electrically
connected and indicated as positively charged. As will be explained
below in this specification, the amount of active LTO material in
the one side of the each of the anode electrodes (the sides facing
the AC capacitors) has been decreased for the purpose of equalizing
the flow of lithium ions during the charging of the hybrid
cell.
FIG. 5A is a simplified schematic side-view of another modified
version of a six-member grouping of battery and capacitor
electrodes in a hybrid cell arrangement. In FIG. 5A, three anode
members utilizing porous layers of LTO particles are
inter-positioned in a specific arrangement with two LMO cathode
members and an AC cathode member. In this embodiment, the AC
cathode member has particles of activated carbon on only one side
of its current collector. The two LTO cathode members positioned on
opposite sides of the AC capacitor have LTO particles on only one
side of their current collector foils. And the LMO cathode
positioned between two LTO anodes has a porous layer of LMO
particles on only one side of its current collector foil. This
modification to the electrode structures is made for the purpose of
reducing the flow of lithium ions between one of the LTO electrodes
and an adjacent capacitor during the charging of the hybrid
cell.
FIG. 5B is a simplified schematic side-view of another modified
version of a six-member grouping of battery and capacitor
electrodes in a hybrid cell arrangement. In FIG. 5B, two LTO anode
members and an AC capacitor member (negatively charged) are
inter-positioned in a specific pattern with two LMO cathode members
and an inter-positioned AC capacitor member (positively charged).
In this embodiment, one LTO anode has particles of LTO on only one
side of its current collector foil, and one LMO cathode has
particles of LMO on only one side of its current collector foil.
Both AC electrodes have a porous layer of particles on only one
side of their current collector foils. Again, this change in the
electrode structures has been made for the purpose of reducing the
flow of lithium ions between two capacitor electrodes and one LTO
electrode and the LMO electrode during the charging of the hybrid
cell.
DESCRIPTION OF PREFERRED EMBODIMENTS
The electrodes of lithium-ion cells are often formed by bonding
particles of active electrode materials that have a largest
dimension in the range of about 0.5 to 30 micrometers to a
compatible metal current collector foil having a thickness of about
5 to 30 micrometers. The particles are bonded in a porous layer of
generally uniform thickness on a major surface of the current
collector foil so that the layer can subsequently be infiltrated
with an electrolyte solution. As stated, the shape of the current
collector is often rectangular with side dimensions that provide a
predetermined surface area to enable it to support a predetermined
quantity of electrode material for a lithium-ion battery electrode
or capacitor electrode member. Each side of the current collector
foil may be coated with a porous layer of particles of electrode
material, but the sustainable thickness of each layer is usually
limited to about 5 .mu.m to 250 .mu.m. In accordance with practices
of this invention, the thicknesses of the layers of active
electrode materials and of the capacitor materials are carefully
determined, for the purpose of enhancing the function of the hybrid
battery and capacitor cells in which the materials are employed. In
some embodiments, one side of the current collector may be left
uncoated for the same purpose.
In a first embodiment of this invention, four different
electrochemical cell units of opposing positively-charged and
negatively-charged porous electrodes of varying compositions of
particulate electrode materials are described. In order to simplify
this general discussion of the respective electrodes, the thickness
of the porous coating layers of battery or capacitor particles may
be visualized without regard to a specified thickness. Combinations
of two or more pairs of these electrodes (cell units) are assembled
for use in forming hybrid lithium-ion battery/capacitor cells in
accordance with one embodiment of this invention. In a hybrid
battery/capacitor electrochemical cell, a predetermined combination
of the pairs of opposing electrodes will be assembled, with
interposed porous separators and the pores of the assembled
electrodes and separators infiltrated with a liquid solution of a
suitable lithium-containing electrolyte.
As stated, in practices of this invention, electrodes are formed of
various combinations particles of capacitor materials and
lithium-ion battery materials. Activated carbon particles are
preferred for use as capacitor materials, whether the electrode in
which they are used is positively or negatively charged.
A few examples of suitable electrode materials for an anode
electrode (negative electrode during discharge of the cell) of a
lithium ion cell are graphite, some other forms of carbon, silicon,
alloys of silicon with lithium or tin, silicon oxides (SiO.sub.x),
metal oxides, and lithium titanate. During cell-discharge,
electrons are released from the anode material into the electrical
power-requiring external circuit and lithium ions are released
(de-intercalated) into an anhydrous lithium ion conducting
electrolyte solution. Typically, lithium-ion cell anode materials
are resin-bonded as a porous layer onto one or both sides of a
copper current collector foil. Lithium titanate particles may be
resin bonded to either a copper current collector foil or to an
aluminum current collector foil. A small amount of conductivity
enhancing carbon particles may be mixed with the anode
particles.
Examples of positive electrode materials (cathode), used in
particulate form, include lithium manganese oxide, lithium nickel
oxide, lithium cobalt oxide, lithium nickel manganese cobalt oxide,
other lithium-metal-oxides, and lithium iron phosphate. Other
materials are known and commercially available. One or more of
these materials may be used in an electrode layer. Typically,
lithium-ion cell cathode materials are resin-bonded to one or both
sides of an aluminum current collector foil. A small amount of
conductivity enhancing carbon particles may be mixed with the
cathode particles.
In addition to activated carbon particles, suitable capacitor
cathode and anode materials include, in particulate form, for
example:
Metal Oxides, MOx, where M=Pb, Ge, Co, Ni, Cu, Fe, Mn, Ru, Rh, Pd,
Cr, Mo, W, Nb.
Metal Sulfides, such as TiS.sub.2, NiS, Ag.sub.4Hf.sub.3S.sub.8,
CuS, FeS, FeS.sub.2.
Other various forms of carbon particles, such as activated carbon
fibers, graphite, carbon aerogel, carbide-derived carbon, graphene,
graphene oxide, and carbon nanotubes. More than one type of carbon
may be used in a blended capacitor material. The same carbon
material may be used in both the anode and cathode in an electric
double-layer capacitor (EDLC).
Particles of one or more of the following polymers may be used as
capacitor material in the cathode of the cell; poly (3-methyl
thiophene), polyaniline, polypyrrole, poly(paraphenylene),
polyacene, polythiophene, and polyacetylene.
The capacitor particles or lithium-ion battery anode particles or
cathode particles are coated or otherwise suitably combined with a
suitable amount of a bonding material. For example, the particles
may be dispersed or slurried with a solution of a suitable resin,
such as polyvinylidene difluoride dissolved in
N-methyl-2-pyrrolidone, and spread and applied to a surface of a
current collector in a porous layer. Other suitable binder resins
include carboxymethyl cellulose/styrene butadiene rubber resins
(CMC/SBR) or polytetrafluoroethylene (PTFE). The binders are not
electrically conducive and should be used in a minimal suitable
amount to obtain a durable coating of porous electrode material
without fully covering the surfaces of the particles of electrode
material.
In many battery constructions, the separator material is a porous
layer of a polyolefin, such as polyethylene (PE), polypropylene
(PP), non-woven, cellulose/acryl fibers, cellulose/polyester
fibers, or glass fibers. Often the thermoplastic material comprises
inter-bonded, randomly oriented fibers of PE or PP. The fiber
surfaces of the separator may be coated with particles of alumina,
or other insulator material, to enhance the electrical resistance
of the separator, while retaining the porosity of the separator
layer for infiltration with liquid electrolyte and transport of
lithium ions between the cell electrodes. The separator layer is
used to prevent direct electrical contact between the facing
negative and positive electrode material layers and is shaped and
sized to serve this function. In the assembly of the cell, the
facing major faces of the electrode material/wire layers are
pressed against the major area faces of the separator membrane. A
liquid electrolyte is typically injected into the pores of the
separator and electrode material layers.
In practices of this invention, metal foil current collectors are
coated on one or both of their major surfaces with porous layers of
individual electrode materials. The thicknesses of the coating
layers are often varied for the purpose of managing the capacity of
the layer to accept and release lithium ions and anions of the
lithium electrolyte solution. In some embodiments of this
invention, an electrode may be coated on both sides with capacitor
particles or anode material particles or cathode material
particles. The thicknesses of the coatings are not necessarily the
same on each side of the current collector. Or one side of the
current collector may remain uncoated with battery or capacitor
particles. The thus prepared electrode materials may be used in
combinations in the assembly of hybrid battery/capacitor cells.
Following are illustrations of such combinations of hybrid
electrodes in battery/capacitor material electrochemical material
cells.
FIG. 1 illustrates the four cell units in side view for the purpose
of showing the two relatively thin porous layers of electrode
particles applied to both sides of a metallic current collector
foil. The current collector foils are typically rectangular in
shape with height and width dimensions suitable for assembly by
stacking or winding into a unitary package of one or more
electrochemical cells. If the finished electrochemical cell is to
be formed of a stacking of two or more cell units (and their
interposed separators) the current collector foils with their
coatings of electrode materials may be nearly square. If the
finished electrochemical cell is to be formed by winding of the
cell units and separators, the foils may be quite long.
In FIG. 1A, a first cell unit 10 is formed of a cathode and an
anode composed for a lithium-ion battery cell. The cell unit 10
includes a first current collector 11 coated on both sides with
thin porous layers of particulate cathode material (e.g., NMC or
LMO) 10' bonded to the major faces of the current collector 11.
Current collector 11 may, for example, be formed of a rectangular
aluminum foil with a suitable connector tab (+) on one side, the
top side in FIG. 1A. In FIG. 1A a second current collector 11'
(e.g., copper foil) is coated on both of its opposing sides with
thin porous layers of particulate anode material 10'' (e.g.,
graphite or LTO). Current collector 11' also has a suitable
connector tab (-) on its top side. In this cell unit, the cathode
is labeled with a plus (+) charge and the anode is labeled with a
minus (-) charge as reflects their state in a charged cell, and as
the cell is being discharged. Facing surfaces of an anode layer
10'' and a cathode layer 10' are placed against a porous separator
18 of like size and shape. Porous separators 18 are typically
formed of polymeric sheets. First cell unit 10 is also described as
Unit A in the Summary section presented above in this
specification.
In FIG. 1B, a second cell unit 12, structurally similar to the
first cell unit 10, is formed of two electrodes, each containing
porous layers of particles of capacitor material 12', 12''. The
electrodes may be formed of like materials but they will experience
opposing charges (plus and minus) in the function of the
electrodes. A first current collector foil (suitably an aluminum
foil) 13 is coated on both of its opposing sides with a porous
layer of, for example, activated carbon particles 12' to form a
positive (+) capacitor electrode. A second current collector foil
13' (suitably a copper foil) is coated on both of its opposing
sides with a porous layer of, for example, activated carbon
particles 12'' to form an electrode which is designated as (-) in
FIG. 1B. The upstanding connector tabs of the respective current
collectors (13, 13') are labeled with the respective positive (+)
and negative (-) charges of the capacitor materials. Facing
surfaces of the respective capacitor layers 12', 12'' are placed
against a porous separator 18 of like size and shape as the
surfaces of the capacitor electrode material. Second cell unit 12
is also described as Unit B in the Summary section presented above
in this specification.
In FIG. 1C, a third cell unit 14 is formed of a positive electrode
of porous layers of cathode material (e.g., particles of LMO or
NMC) 14' bonded to both sides of a current collector foil (e.g. an
aluminum foil) 15. The third unit cell also includes a negative
electrode formed of porous layers of particles of capacitor
material 14'' bonded to both sides of a copper current collector
foil 15'. Again, the respective charges of the cathode material (+)
and the capacitor material (-) are indicated on the upstanding
connector tabs of their respective current collector foils (15,
15'). Facing surfaces of cathode material 14' and of capacitor
material 14'' are placed against opposite faces of a porous
separator 18. Third cell unit 14 is also described as Unit C in the
Summary section presented above in this specification
The fourth cell unit 16 (FIG. 1D) is formed of a positive electrode
of porous layers of capacitor particles 16' bonded to both sides of
a current collector foil 17. The capacitor particles may be
particles of activated carbon. The fourth cell unit in this
embodiment of the invention also includes a negative electrode of
porous layers of anode material 16'' (e.g., graphite or LTO
particles) bonded to both sides of a current collector foil 17'.
The respective charges of the capacitor material (+) and the anode
material (-) in the charged state of the cell unit are indicated on
the upstanding connector tabs of their respective current collector
foils (17, 17'). Facing surfaces of capacitor particles 16'' and of
anode material 16' are placed against opposite faces of a porous
separator 18. Fourth cell unit 16 is also described as Unit D in
the Summary section presented above in this specification
The above described four cell units are used in combinations of at
least two of the units (or more) and such that at least one
capacitor electrode (positive or negative) is used in combination
with battery anodes and cathodes. In each such combination of cell
units, they will be assembled as stacks or wound rolls with
interposed porous separator layers. And the pores of the electrode
layers and separators will be infiltrated with a non-aqueous liquid
electrolyte conductive of lithium cations and compatible anions.
When desired, each of these new hybrid electrochemical cells may be
combinations of two or more of the hybrid cells and the combined
cells may be interconnected in parallel or series connection to
obtain a hybrid mixture of lithium-ion battery and capacitor
electrodes that provide a desired combination of energy and power
characteristics.
The electrolyte for a subject hybrid lithium-ion battery/capacitor
cell may be a lithium salt dissolved in one or more organic liquid
solvents. Examples of suitable salts include lithium
hexafluorophosphate (LiPF.sub.6), lithium tetrafluoroborate
(LiBF.sub.4), lithium perchlorate (LiClO.sub.4), lithium
hexafluoroarsenate (LiAsF.sub.6), and lithium
trifluoroethanesulfonimide. Some examples of solvents that may be
used to dissolve the electrolyte salt include ethylene carbonate,
dimethyl carbonate, methylethyl carbonate, propylene carbonate.
There are other lithium salts that may be used and other solvents.
But a combination of lithium salt and solvent is selected for
providing suitable mobility and transport of lithium ions in the
operation of the hybrid cell with its battery and capacitor
electrode combinations. The electrolyte is carefully dispersed into
and between closely spaced layers of the electrode elements and
separator layers.
In general, it is preferred to combine cell units to form a hybrid
electrochemical cell producing an energy density in the range of 20
Wh/kg to 200 Wh/kg and a power density in the range of 500 W/kg and
10,000 W/kg. Values of energy density and power density depend on
the composition of the battery electrode materials and of the
capacitor electrode materials, and on the ratio of contents of
battery electrode materials and capacitor electrode materials. In
general energy density is improved by increasing battery material
content and/or by selecting high specific energy battery electrode
materials. And the power density of the hybrid electrochemical cell
is increased by increasing the content of capacitor electrode
material and/or by selecting high specific power density capacitor
compositions. The use of combinations of the subject four-unit cell
units is a convenient and effective method of preparing and using
building units to produce one or more hybrid electrochemical cells
having a desired combination of energy density and power density
properties.
In FIG. 2A, a first hybrid electrochemical cell is illustrated. In
this example, the hybrid electrochemical cell is formed by a
combination of cell unit 10 (as described with respect to FIG. 1A)
with cell unit 16 (as described with respect to FIG. 1D). This
hybrid electrochemical cell (10, 16) comprises a positive electrode
of cathode material 10' and a positive capacitor electrode 16' and
two negative electrodes 10'', 16'' of anode material for a
lithium-ion cell. An additional porous separator 18 is placed
between the unit cell units 10, 16. The connector tabs of the
positively charged capacitor material and the cathode material are
to be interconnected in parallel combination. And the two connector
tabs of negatively charged anode material are to be interconnected
in parallel connection. The shapes of the respective layered
electrodes will enable them to be assembled in stacks or wound
rolls in forming the hybrid electrochemical cell (10, 16). In this
example, the combination of the positively-charged capacitor
electrode 16' with the positively charged cathode material 10', and
the opposing two negatively-charged anode electrodes 10'', 16'',
alters the power characteristics of the cell in favor of the
negative electrodes. Thus, the compositions, thickness, and
cross-sectional areas of the electrodes can be varied to provide
predetermined energy and power density characteristics of this
hybrid electrochemical cell (10, 16).
In FIG. 2B, a different hybrid electrochemical cell is illustrated.
In this example, the hybrid electrochemical cell is formed by a
combination of cell unit 10 with two cell units 14. The resulting
assembly of cell units (14, 14, 10) produces a hybrid
electrochemical cell comprising three connected positively charged
cathode members 10', 14', 14' in combination with one negatively
charged anode 10'' and two negatively charged capacitor electrodes
14''. Each group of three like-charged electrode members would be
electrically connected in parallel in the operation of the hybrid
cell.
It is noted that the capacitor material is used in a positive
electrode in the example of FIG. 2A and in a negative electrode in
the example of FIG. 2B. Assuming that each of the anode material,
cathode material, and capacitor material are the same in the two
hybrid cell examples, it is expected that the energy of the FIG. 2B
cell will be higher than the energy of the FIG. 2A cell.
In FIG. 2C, the hybrid electrochemical cell comprises four unit
cells--14, 16, 16, 12. As illustrated in FIG. 2C, this combination
of unit cells produces a hybrid electrochemical cell formed of a
single positively-charged cathode with three positively-charged
capacitor electrodes in combination with two negatively charged
anodes and two negatively charged capacitor electrodes. Each group
of five like-charged electrode members would be electrically
connected in parallel in the operation of the hybrid cell. Thus,
this hybrid cell (14, 16, 16, 12) is provided with five capacitor
electrodes and an unbalanced number (3) of lithium-ion battery
electrodes. Such a combination of properly composed and sized
electrodes can provide substantial power density properties in the
resulting hybrid cell or combination of like hybrid cells.
FIG. 3A is a schematic side-view or edge-view of a modified version
of the hybrid grouping of FIG. 2A. In FIG. 3A, two lithium titanate
(LTO) anodes are paired with a lithium manganese oxide (LMO)
battery cathode and an activated carbon (AC) capacitor cathode. The
LTO anode members are electrically connected in parallel and
indicated as negatively charged as they would be when the hybrid
cell is being discharged. The LMO battery cathode and AC capacitor
cathode are electrically connected in parallel and indicated as
positively charged. Although not apparent from the side views, each
of the electrodes is of like rectangular shape with their applied
porous layers of electrode material covering most of the major
surfaces of the respective current collectors except for the tabs
on one side of the rectangular foil, used for electrical connection
with other electrode members. The thicknesses of the current
collector foils is typically in the range of about seven to twenty
micrometers. The thicknesses of the respective applied electrode
layers may be varied to provide the desired electrochemical
capacity of the electrode material.
In this example, each of the electrodes is formed with a porous
resin-bonded coating of the indicated electrode material on each
side of a current collector foil. The two LTO anodes have particles
of lithium titanate bonded as a porous layer of substantially
uniform thickness on each side of a copper current collector foil.
The LMO cathode has a porous layer of lithium manganese oxide
particles bonded as a porous layer on each major surface of an
aluminum current collector foil. And the capacitor (AC) is formed
of a porous layer of substantially uniform thickness of activated
carbon particles resin bonded to each side of an aluminum current
collector foil. In this example, one LTO anode (to the left in FIG.
3A) has been stacked between the LMO cathode and the AC capacitor.
The second LTO anode is stacked on the opposite side of the AC
capacitor electrode. In this assembly of cell members, like-shaped,
porous separator members (not illustrated to simplify the figure)
would be placed between each of the surfaces of the electrode
materials, and also on the outer face (as viewed in FIG. 3A) of the
LMO cathode and the outer face of the outer LTO anode. The porous
electrode material layers and the porous separators would be
stacked closely together and suitably infiltrated with a
non-aqueous liquid electrolyte solution of a lithium electrolyte
composition, such as LiPF.sub.6.
Under the influence of a cell-charging, direct current (during
which the LTO anodes are positively charged) is passed through the
hybrid cell of FIG. 3A. Lithium ions are released from the LMO
cathode and the AC capacitor and driven under the charging
potential through the liquid electrolyte into the lithium titanate
particles. Lithium ions from the LMO electrode are transported most
directly into side 1 of the LTO anode assembled on the left side of
the FIG. 3A hybrid cell. Lithium ions are also transported from
side 3 of the enhanced-size AC capacitor (which is negatively
charged during cell charging) to side 2 of the LTO anode. Further,
lithium ions are desorbed from side 4 of the AC capacitor to sides
5 and 6 of the LTO anode assembled on the right side of the hybrid
cell of FIG. 3A. When the lithium titanate content on both sides of
an LTO anode are about the same, it is preferred that each side of
anode material receive the same appropriate, balanced amount of
lithium ions.
The lithium titanate composition is chemically capable of receiving
lithium ions during charging and incorporating the lithium in the
lithium titanate composition of the anode material. As may be
obtained from LTO material data, or determined experimentally, the
total weight (or molar content) of lithium titanate particles in
each LTO anode is capable of receiving (intercalating) a known
quantity of lithium during a charging cycle. And the applied
charging potential and duration is managed such that the anode
material can assimilate the lithium ions into the micrometer size
LTO particles without an imbalance of lithium being accumulated on
or around the LTO particles. In general, a known amount of lithium
can be received from the combination of the LMO cathode particles
and AC capacitor particles.
It is to be recognized that during discharge of the hybrid cell,
lithium ions are released from both sides of the LTO electrodes (of
FIG. 3A). Some of the lithium ions are transported back through the
electrolyte and intercalated into the LMO cathode particles. The
balance of the lithium ions, released during cell discharge, are
intended to associate with anions (PF.sub.6.sup.-) released by the
AC capacitor particles. In the operation of this cell, the AC
capacitor particles absorb PF.sub.6.sup.- anions during charging of
the hybrid cell and release the anions during discharge of the
cell. The amount of AC capacitor particles must be managed for it
adsorb and release a sufficient number of anions to enable the LTO
electrodes and the LMO electrode to accept and release their
intended amounts of lithium ions. In the schematic illustration of
FIG. 3A, the amount of capacitor material has been increased to
serve its required anion absorbing and desorbing function.
As stated above in this specification, the capacitor particles
typically accept less anions per unit weight or molar unit than the
amount of lithium ions accepted by particles of battery material.
In order to avoid imbalances of lithium ions throughout the
materials of the hybrid cell, it is preferred, and often necessary,
to provide a suitable, predetermined balance in battery electrode
material particles and capacitor material particles. This balance
enables the hybrid cell to display columbic efficiency and maintain
its capacity and functional life. In this practice of the operation
of the hybrid electrochemical cells of this disclosure, it is
necessary to seek and find a suitable balance between the
capacities of each battery electrode and a capacitor electrode
between which lithium ions are exchanged during cycling of the
hybrid cell. This typically involved balance the weights or molar
amounts of such lithium ion exchanging battery and capacitor
materials.
In the hybrid cell configuration of FIG. 3A, it is intended that
lithium ions will be transported through the liquid electrolyte
solution so as to reach each deposited layer of the opposing bodies
of electrode materials. Lithium ions released by amount of active
anode material in the two LTO anodes must be effectively accepted
into the LMO cathode and the AC cathode. Accordingly, the
respective amounts of electrode materials must be suitably balanced
to achieve this result. In this example, the amount of anode and
cathode battery materials are pre-determined and the amount of AC
capacitor particles are then determined in view of the set lithium
ion accepting capacities of the LTO and LMO materials. Thus, the
relative thicknesses (reflecting weights or molar amounts) of the
LMO electrode and two LTO electrodes are indicated schematically in
FIG. 3A. In general, this requires an amount of activated carbon
particles leading to thicker layers (labeled 3,4) of capacitor
material on the AC cathode member in FIG. 3A, as compared with the
thicknesses (also reflecting weight or molar amounts) of the
lithium titanate particles (labelled 1,2 on the centered LTO
electrode). In this hybrid cell arrangement, it is preferred that
the capacity (C) of side 2 of the LTO electrode to accept lithium
ions be equivalent to 0.8-1.2 C of the of side 3 of the AC cathode.
The same proportioning of capacities would also apply to the
activated carbon content of side 4 of the AC capacitor electrode
with the facing side 5 of the LTO electrode to its right in FIG.
3A.
FIG. 3B is a modified and simplified side-view or edge-view of the
hybrid cell grouping of FIG. 2B. In the hybrid cell arrangement of
FIG. 3B, a LTO anode, an AC capacitor, and a second LTO anode are
electrically connected in parallel arrangement, indicated as
negatively charged. Inserted between them are an LMO cathode, an AC
capacitor, and a second LMO cathode, connected in parallel and
indicated as positively charged. As illustrated in FIG. 3B, side 2
of one of the LTO anodes is facing side 3 of an oppositely charge
AC capacitor. And side 7 of an LMO cathode is facing side 6 of a
different AC capacitor. The lithium-accepting capacities of the LTO
anodes and the LMO cathodes are predetermined and are substantially
equivalent. However, the relative amounts of the oppositely-charged
AC capacitor members were increased such that the activated carbon
capacitor materials had sufficient capacity to receive lithium
cations and the corresponding anions (e.g., PF.sub.6.sup.-) in the
repeated charging and discharging of the hybrid cell. In this
example, the relative capacities (C) of the electrode materials
(with reference to the numbered electrode layers in FIG. 3B) are as
follows: C.sub.LMO-7=C.sub.AC-6 and
C.sub.LTO-2/C.sub.AC-3=0.8-1.2.
The hybrid cell arrangements in FIGS. 4A and 4B are like those
respectively in FIGS. 3A and 3B, but lithium ion accepting
capacities of the battery materials and the capacitor materials
have been balanced in a different manner. In these examples, the
amount of battery electrode material is reduced on one side of a
LTO anode or a LMO cathode in order balance the lithium ion
assimilating capacity of a pre-set AC capacitor.
In FIG. 4A, two LTO anodes, connected in parallel and indicated
with a negative charge, are interposed with an LMO cathode and an
enlarged AC capacitor, connected in parallel and indicated with a
positive charge. In this example, the current capacity of the AC
capacitor electrode is about 30% of the capacities of the facing
sides of the LTO electrodes. Again, in FIG. 4A, the LTO anodes are
positioned on opposite sides of the enlarged AC capacitor. In FIG.
4A, the sides of the LTO electrodes, labelled LTO-2, are facing
opposite sides of the two-side coated AC capacitor. The opposite
sides of the LTO electrodes are labelled LTO-1. In this example,
the loadings of lithium titanate particles are reduced on the LTO-2
sides of the anodes in order to balance the lithium assimilating
capacity of the hybrid cell, including the AC capacitor. The
loadings of lithium titanate particles on the current collectors
were asymmetric. The loading ratios of the lithium titanate
particles on the sides of the LTO electrodes are respectively,
LTO-2/LTO-1=0.2-0.5.
In the hybrid cell arrangement of FIG. 4B, a LTO anode, an AC
capacitor, and a second LTO anode are electrically connected in
parallel arrangement, indicated as negatively charged. Inserted
between them are an LMO anode, an AC capacitor, and a second LMO,
connected in parallel and indicated as positively charged. In this
hybrid cell arrangement of FIG. 4B, the positively charged AC
capacitor and the negatively-charged AC capacitor are placed next
to each other. The positively charged AC also faces an LTO anode
(with sides labelled 1,2 in FIG. 4B) and the negatively charged AC
also faces a positively charged LMO cathode (with sides labelled
3,4). In this example, the loading of lithium titanate particles on
side LTO-2 are reduced and the loading of lithium manganese oxide
particles on side LMO-3 are reduced to balance the capacities of
the respective electrodes of the hybrid cell to assimilate lithium
ions.
The loading ratios of the lithium manganese oxide particles on the
sides of the LMO electrodes are LMO-3/LMO-4=0.2-0.5. And the
loading ratios of the lithium titanate particles on the sides of
the LTO electrodes are respectively, LTO-2/LTO-1=0.2-0.5.
FIGS. 5A and 5B illustrate the use of a single sided battery
electrode with an optimized capacity ratio (for absorbing lithium
ions) between a lithium ion battery electrode and a capacitor
electrode.
FIG. 5A illustrates a hybrid cell formed of three LTO anode
members, electrically connected in parallel, and indicated as
negatively charged. The anode members are interposed with two LMO
cathode members and a central AC capacitor member. As illustrated,
the AC capacitor is placed between two of the three LTO anodes. In
order to balance the lithium ion absorbing capacities of the
respective members of the hybrid cell, the AC capacitor is formed
with a coating on only one side of its current collector and the
LTO anodes on the sides of the AC capacitor are also single
side-coated. Further, a one side-coated LMO cathode is positioned
facing a one side-coated LTO anode. As illustrated in FIG. 5A, the
uncoated side of the AC capacitor faces an uncoated side of a one
side-coated LTO anode. And the coated side of the AC capacitor
(labelled 1) faces the coated side (labelled 2) of the one
side-coated LTO cathode. The only two side coated electrodes in
this hybrid cell embodiment are the outer placed LMO cathode and
LTO anode.
In order to balance the lithium ion absorbing capacities (C) of the
electrodes of the hybrid cell, it is preferred that
C.sub.LTO-2/C.sub.AC-1=0.8-1.2. This balance of capacities between
facing coated sides of the specified LTO electrode and the only
capacitor electrode serves to avoid unwanted rebalance reactions of
lithium ions at the respective electrodes. In this arrangement of
anode electrodes facing a capacitor electrode, the specified N/P
ratio serves to balance the movement of lithium ions in this hybrid
cell arrangement.
FIG. 5B illustrates a hybrid cell formed of an assembly of two
outer LTO anode members (one of which is one side coated with
lithium titanate particles) with a one side-coated AC capacitor
member between them. They are electrically connected in parallel
and indicated as negatively charged. The interposed cathode members
consist of two outer LMO cathodes (one of which is one side-coated)
with a one side-coated AC capacitor between them. As illustrated
the negatively-charged and positively-charged one side-coated AC
capacitors (respectively labelled 2 and 3) are placed side by side
(with an intervening separator, not illustrated) with a one
side-coated LTO anode (labelled 1) and a one side-coated LMO
cathode opposite their outer uncoated surfaces. The active carbon
particle coated surfaces of the AC cathodes (labelled 2 and 3) face
toward each other (through a separator, not illustrated) in the
assembled cell.
In order to balance the lithium ion absorbing capacities (C) of the
electrodes of the hybrid cell, it is preferred that
C.sub.AC-2=C.sub.AC-3 and C.sub.LTO-1/C.sub.AC-2=0.8-1.2. Again,
this balance of capacities between of the battery electrodes and
the capacitor serves to avoid unwanted rebalance reactions of
lithium ions at the respective electrodes. In this arrangement of
anode electrodes facing a capacitor electrode, the specified N/P
ratio serves to balance the movement of lithium ions in this hybrid
cell arrangement.
The above specific examples are intended to illustrate practices of
the invention, but these illustrations are not limitations on the
scope of the invention. It is clear that the above described basic
hybrid electrodes and hybrid combinations of electrodes may be
readily prepared and combined to make widely different useful
hybrid electrochemical cells with different combinations and
balances of battery and capacitor properties.
* * * * *